If you're talking about buying a domain name from an ICANN accredited facility that's 10 miles away from you, rather than 1,000 miles.. I don't think that will ever be a ranking factor.
Now, a .co.uk WILL outrank a .com domain name in the UK market. Country specific domains have a much eaiser time ranking in the various contry specific Google search pages.
For that reason, we have our .COM which is our main site, and a .CO.UK which is our UK version hosted on UK servers in the UK.
So domain extension will make a difference, but the registrar that purchased the domain name - that will likely never play a roll.. at least I hope not!